Updates in the treatment of asthma in pediatrics: A review for pharmacists

PURPOSE

The purpose of this review is to summarize the management of asthma in children and to highlight different guideline-based approaches. This review also discusses literature regarding the use of corticosteroids, both inhaled and systemic, as well as biologic agents, in asthma management.

SUMMARY

Asthma is a common chronic respiratory condition in the pediatric population and has evolved into a highly patient-specific disease. Of the 2 main asthma guidelines, one developed by the National Asthma Education and Prevention Program was recently published as a focused update in 2020. The other, from the Global Initiative for Asthma, focuses on a global strategy for management and prevention, with the most recent update in 2023. Both reports discuss diagnosis, assessment, and treatment of asthma in adults and children. Treatment is designed as a stepwise approach in both reports, although there are key differences. This article focuses on gaps in these guidelines, including the use of bronchodilators and inhaled corticosteroids with single maintenance and reliever therapy and long-acting muscarinic antagonists in children. It also reviews treatment in children under 5 years of age, although recommendations are limited due to a lack of evidence in this age group. Finally, this review discusses considerations for emerging treatments, including biologics, for patients who are difficult to treat.

CONCLUSION

New treatment strategies and agents have emerged in the treatment of pediatric asthma. Pharmacists play a key role in providing education about, dispensing, and recommending the newest evidence-based treatment options for children.

Ommaya reservoir use in pediatric ALL and NHL: a review at St. Jude Children's Research Hospital

PURPOSE

The intraventricular route of chemotherapy administration, via an Ommaya Reservoir (OmR) improves drug distribution in the central nervous system (CNS) compared to the more commonly used intrathecal administration. We retrospectively reviewed our experience with intraventricular chemotherapy, focused on methotrexate, in patients with Acute Lymphoblastic Leukemia (ALL) and Non-Hodgkin Lymphoma (NHL).

METHODS

Twenty-four patients (aged 7 days - 22.2 years) with 26 OmR placements were identified for a total of 25,009 OmR days between 1990 and 2019. Methotrexate cerebrospinal fluid (CSF) concentrations (n = 124) were analyzed from 59 courses of OmR therapy in 15 patients. Twenty-one courses involved methotrexate dosing on day 0 only, whereas 38 courses involved booster dosing on days 1, 2, or both. We simulated the time CSF methotrexate concentrations remained > 1 µM for 3 days given various dosing regimens.

RESULTS

CSF methotrexate exposure was higher in those who concurrently received systemic methotrexate than via OmR alone (p < 10- 7). Our simulations showed that current intraventricular methotrexate boosting strategy for patients ≥ 3 years of age maintained CSF methotrexate concentrations ≥ 1 µM for 72 h 40% of the time. Alternatively, other boosting strategies were predicted to achieve CSF methotrexate concentrations ≥ 1 µM for 72 h between 46 and 72% of the time.

CONCLUSIONS

OmR were able to be safely placed and administer intraventricular methotrexate with and without boost doses in patients from 7 days to 22 years old. Boosting strategies are predicted to increase CSF methotrexate concentrations ≥ 1 µM for 72 h.

Evaluation of Continuous Infusion Vancomycin in a Pediatric Hematology/Oncology Population

BACKGROUND

Continuous infusion vancomycin (CIV) may benefit children who are unable to achieve therapeutic concentrations with intermittent vancomycin dosing and may facilitate outpatient administration by alleviating the burden of frequent dosing intervals. Previous studies have used variable dosing regimens and steady-state concentration goals. The purpose of this study was to evaluate the total daily dose (TDD) of CIV required to achieve therapeutic steady-state concentrations of 15-25 µg/mL in pediatric hematology/oncology patients.

METHODS

A single-center retrospective study was performed for patients treated with CIV from January 2017 to June 2019. The primary outcome was the TDD required to achieve therapeutic steady-state concentrations on CIV. Secondary outcomes included time to reach therapeutic steady-state concentrations, CIV indications and adverse events associated with CIV.

RESULTS

Data were collected for 71 courses of CIV in 60 patients. Median patient age was 4 years (range: 0.4-20 years). The median TDD required to achieve initial therapeutic concentrations was 50.3 mg/kg/d (interquartile range: 38.8-59.2) and was further divided into age-based cohorts. TDD in mg/kg was significantly lower in the older cohort (P < 0.001), but there was no statistically significant difference between age-based cohorts with TDD in mg/m2 (P = 0.97). Median time to achieve first therapeutic concentration was 19.3 hours (range: 8.6-72.3 hours). The most common indication for CIV was ease of outpatient administration (69.0%). Acute kidney injury incidence was minimal (4.2%).

CONCLUSIONS

CIV is associated with rapid attainment of target concentrations in pediatric hematology/oncology patients and is safe and well tolerated.

Pharmacist Effect on Discharge Follow-Up Education in Pediatric Oncology Outpatient Clinics: A Quality Improvement Study

OBJECTIVE

We aimed to describe the effect of education provided by a clinical pharmacy specialist at a patient's follow-up appointment after discharge, and to assess caregiver satisfaction.

METHODS

A single-center, quality improvement study was conducted. A standardized data collection tool was created to characterize interventions made by clinical pharmacy specialists during an outpatient clinic appointment scheduled shortly after discharge. Pediatric patients with cancer who met the following criteria were included: 1) initial diagnosis without receiving chemotherapy, 2) first course of chemotherapy after initial diagnosis or relapsed disease, and 3) post-hematopoietic stem cell transplantation or cellular therapy. A survey was provided to families after the follow-up discharge appointment to assess the caregiver's satisfaction of the new process.

RESULTS

From January to May 2021, a total of 78 first-time discharge appointments were completed. The most common reason for follow-up was discharge after first course of chemotherapy (77%). The average duration of each appointment was 20 minutes (range, 5-65). The clinical pharmacy specialist made an intervention during 85% of appointments. The most common intervention made during the visit was reinforcement of medications (31%). Thirteen surveys were completed by caregivers; 100% of the caregivers reported the follow-up appointment was helpful. Additionally, they reported the most useful resource provided at discharge was the medication calendar (85%).

CONCLUSIONS

Investing clinical pharmacy specialist time with patients and caregiver after discharge appears to have a meaningful effect on patient care. Caregivers report this process is helpful in better understanding their child's medications.

Just DOAC: Use of direct-acting oral anticoagulants in pediatrics

PURPOSE

The aim of this article is to provide an overview of the current literature for direct-acting oral anticoagulant (DOAC) use in pediatric patients and summarize ongoing trials.

SUMMARY

In treatment of venous thromboembolism (VTE) in pediatric patients, evidence supports use of both dabigatran and rivaroxaban. Dabigatran has been shown to be noninferior to standard of care (SOC) in terms of efficacy, with similar bleeding rates. Similarly, treatment with rivaroxaban in children with acute VTE resulted in a low recurrence risk and reduced thrombotic burden, without increased risk of bleeding, compared to SOC. Treatment of pediatric cerebral venous thrombosis as well as central venous catheter-related VTE with rivaroxaban appeared to be both safe and efficacious and similar to that with SOC. Dabigatran also has a favorable safety profile for prevention of VTE, and rivaroxaban has a favorable safety profile for VTE prevention in children with congenital heart disease. Many studies with several different DOACs are ongoing to evaluate both safety and efficacy in unique patient populations, as well as VTE prevention.

CONCLUSION

The literature regarding pediatric VTE treatment and prophylaxis is growing, but the need for evidence-based pediatric guidelines remains. Additional long-term, postauthorization studies are warranted to further elucidate safety and efficacy in clinical scenarios excluded in clinical trials. Additional data on safety, efficacy, and dosing strategies for reversal agents are also necessary, especially as the use of DOACs becomes more common in the pediatric population.

Evaluation of Aminophylline for the Treatment of Acute Kidney Injury in Pediatric Hematology/Oncology Patients

OBJECTIVE

The purpose of this study was to compare acute kidney injury (AKI)-related outcomes of patients who received aminophylline in addition to standard of care with matched historical controls who received standard of care alone.

METHODS

This was a single center, retrospective, historical control cohort study that included patients treated for AKI. Patients who received aminophylline from January 2017 to June 2018 were matched for age, sex, primary diagnosis, and hematopoietic cell transplant history in a 1:2 ratio to historical controls treated for AKI from July 2015 to September 2016. The primary outcome was improvement in AKI stage at 5 and 10 days from treatment initiation.

RESULTS

Twenty-seven patients who received aminophylline were matched to 54 historical controls. Fifty-eight patients (72%) had recently undergone hematopoietic cell transplant. At day 5, improvement in AKI stage was observed in 56% of patients in each group (p = 1.0); at day 10, improvement in AKI stage was observed in 75% of patients in the aminophylline group vs 70% of historical controls (p = 0.76). By day 10, serum creatinine levels had returned to baseline in 21% of patients in the aminophylline group and 34% of patients in the control group (p = 0.37).

CONCLUSIONS

Findings of this study demonstrated no difference in the rate of AKI resolution or in the proportion of patients with resolved AKI when aminophylline was added to standard of care for the treatment of AKI in this pediatric hematology/oncology population.

Experience using intravenous posaconazole in paediatric and young adult oncology patients

BACKGROUND

Posaconazole exhibits broad-spectrum antifungal activity. An IV formulation became available in 2014. Few studies describing the use of this formulation exist in patients under the age of 18 years. This study describes our experience using IV posaconazole in paediatric and young adult cancer patients.

METHODS

This single-centre retrospective chart review evaluated patients who received IV posaconazole and had at least one posaconazole plasma concentration obtained after five or more days with a consistent dosage. Relationships between doses required to achieve a plasma concentration of ≥1 µg/mL and patient age, weight and body surface area (BSA) were evaluated. The clinical record was reviewed to identify descriptions of any adverse events.

RESULTS

Twenty-five patients were analysed, with a median age of 10.5 years (range 1.9-22.9 years; 92% were <18 years). All patients were able to achieve a posaconazole plasma concentration ≥1 µg/mL during their treatment course. The daily mg/kg/day dose required to achieve the target concentration decreased significantly with increasing age of the patient (P = 0.018). Assessment of dosage based on BSA suggested a requirement of 225 mg/m2/day across all age groups <18 years. Adverse events documented in the clinical record were consistent with those described with the oral formulations. No CNS toxicities were observed with use of IV posaconazole.

CONCLUSIONS

Concentrations ≥1 µg/mL are achievable and a BSA-based dosing approach may allow a consistent empirical dose for patients <18 years of age. Therapeutic drug monitoring is recommended to ensure patients achieve therapeutic concentrations.

Consensus Guideline for Use of Glucarpidase in Patients with High-Dose Methotrexate Induced Acute Kidney Injury and Delayed Methotrexate Clearance

An expert panel was convened to provide specific, expert consensus guidelines for the use of glucarpidase in patients who develop high‐dose methotrexate (HDMTX)‐induced nephrotoxicity and delayed methotrexate excretion. This guideline provides recommendations to identify the population of patients who would benefit from glucarpidase rescue by more precisely defining the absolute methotrexate concentrations associated with risk for severe or life‐threatening toxicity at several time points after the start of a HDMTX infusion.

Acute kidney injury due to high‐dose methotrexate (HDMTX) is a serious, life‐threatening toxicity that can occur in pediatric and adult patients. Glucarpidase is a treatment approved by the Food and Drug Administration for high methotrexate concentrations in the context of kidney dysfunction, but the guidelines for when to use it are unclear. An expert panel was convened to provide specific, expert consensus guidelines for the use of glucarpidase in patients who develop HDMTX‐induced nephrotoxicity and delayed methotrexate excretion. The guideline provides recommendations to identify the population of patients who would benefit from glucarpidase rescue by more precisely defining the absolute methotrexate concentrations associated with risk for severe or life‐threatening toxicity at several time points after the start of an HDMTX infusion. For an HDMTX infusion ≤24 hours, if the 36‐hour concentration is above 30 µM, 42‐hour concentration is above 10 µM, or 48‐hour concentration is above 5 µM and the serum creatinine is significantly elevated relative to the baseline measurement (indicative of HDMTX‐induced acute kidney injury), glucarpidase may be indicated. After a 36‐ to 42‐hour HDMTX infusion, glucarpidase may be indicated when the 48‐hour methotrexate concentration is above 5 µM. Administration of glucarpidase should optimally occur within 48–60 hours from the start of the HDMTX infusion, because life‐threatening toxicities may not be preventable beyond this time point.

Implications for Practice.

Glucarpidase is a rarely used medication that is less effective when given after more than 60 hours of exposure to high‐dose methotrexate, so predicting early which patients will need it is imperative. There are no currently available consensus guidelines for the use of this medication. The indication on the label does not give specific methotrexate concentrations above which it should be used. An international group of experts was convened to develop a consensus guideline that was specific and evidence‐based to identify the population of patients who would benefit from glucarpidase.

Derivation of new equations to estimate glomerular filtration rate in pediatric oncology patients

BACKGROUND AND OBJECTIVE

Monitoring renal function is critical in treating pediatric patients, especially when dosing nephrotoxic agents. We evaluated the validity of the bedside Schwartz and Brandt equations in pediatric oncology patients and developed new equations for estimated glomerular filtration rate (eGFR) in these patients.

METHODS

A retrospective analysis was conducted comparing eGFR using the bedside Schwartz and Brandt equations to measured GFR (mGFR) from technetium-99m diethylenetriamine pentaacetic acid (^99mTc-DTPA) between January 2007 and August 2013. An improved equation to estimate GFR was developed, simplified, and externally validated in a cohort of patients studied from September 2013 to June 2015. Carboplatin doses calculated from ^99mTc-DTPA were compared with doses calculated by GFR-estimating equations.

RESULTS

Overall, the bedside Schwartz and Brandt equations did not precisely or accurately predict measured GFR (mGFR). Using a data subset, we developed a five-covariate equation, which included height, serum creatinine, age, blood urea nitrogen (BUN), and gender, and a simplified version (two-covariates), which contained height and serum creatinine. These equations were used to estimate GFR in 2036 studies, resulting in precise and accurate predictors of mGFR values. Equations were validated in an external cohort of 570 studies; both new equations were more accurate in calculating carboplatin doses than either the bedside Schwartz or Brandt equation.

CONCLUSIONS

Two new equations were developed to estimate GFR in pediatric oncology patients, both of which did a better job at estimating mGFR than published equations.

Sequential administration of methotrexate and asparaginase in relapsed or refractory pediatric acute myeloid leukemia

BACKGROUND

The efficacy of combination chemotherapy with methotrexate (MTX) and asparaginase is not well known in relapsed and refractory acute leukemia after contemporary therapy.

PROCEDURE

A retrospective study of pediatric patients with relapsed or refractory acute myeloid leukemia (AML) who received MTX and asparaginase as a salvage therapy at St. Jude Children Research Hospital was performed. MTX was given intravenously followed by a dose of asparaginase intramuscularly or intravenously 24 hours later. The chemotherapy cycle was repeated every 7-10 days. Response, survival, and toxicities were evaluated.

RESULTS

Fifteen patients, median age 10.5 years (range, 1.1-18.5 years), were treated. Median number of previous therapeutic regimens was three (range, 1-4). Six patients responded to treatment (three had morphologic complete remission with incomplete blood count recovery, two had partial remission, and one had stable disease for 16 months), and four are still alive. Three of six responders had monoblastic leukemia, and also developed tumor lysis syndrome. The 1- and 2-year overall survival rates are 35.6% and 17.8%, respectively. The most common adverse event was transient elevation of transaminases (nine patients). Two patients developed pancreatitis. Episodes of febrile neutropenia were rare (two patients), and most courses (75 out of 93 total courses) were given in an outpatient setting.

CONCLUSIONS

Combination chemotherapy with MTX and asparaginase appears to be an effective salvage therapy and well tolerated in patients with relapsed or refractory childhood AML, even in those heavily pretreated with contemporary frontline or salvage therapy.

Between-course targeting of methotrexate exposure using pharmacokinetically guided dosage adjustments

PURPOSE

It is advantageous to individualize high-dose methotrexate (HDMTX) to maintain adequate exposure while minimizing toxicities. Previously, we accomplished this through within-course dose adjustments.

METHODS

In this study, we evaluated a strategy to individualize HDMTX based on clearance of each individual's previous course of HDMTX in 485 patients with newly diagnosed acute lymphoblastic leukemia. Doses were individualized to achieve a steady-state plasma concentration (Cpss) of 33 or 65 μM (approximately 2.5 or 5 g/m(2)/day) for low- and standard-/high-risk patients, respectively.

RESULTS

Individualized doses resulted in 70 and 63 % of courses being within 20 % of the targeted Cpss in the low- and standard-/high-risk arms, respectively, compared to 60 % (p < 0.001) and 61 % (p = 0.43) with conventionally dosed therapy. Only 1.3 % of the individualized courses in the standard-/high-risk arm had a Cpss greater than 50 % above the target compared to 7.3 % (p < 0.001) in conventionally dosed therapy. We observed a low rate (8.5 % of courses) of grade 3-4 toxicities. The odds of gastrointestinal toxicity were related to methotrexate plasma concentrations in both the low (p = 0.021)- and standard-/high-risk groups (p = 0.003).

CONCLUSIONS

Individualizing HDMTX based on the clearance from the prior course resulted in fewer extreme Cpss values and less delayed excretion compared to conventional dosing.

Posaconazole therapeutic drug monitoring in pediatric patients and young adults with cancer

BACKGROUND

Limited information exists regarding the use of posaconazole for treating systemic fungal infections in children, adolescents, and young adults with cancer. At St. Jude Children's Research Hospital, the recommended posaconazole dose in patients weighing less than 34 kg is 18-24 mg/kg daily, given in 4 divided doses. For patients aged 13 years or older or those weighing 34 kg or more, the recommended dose is 800 mg daily, given orally in 4 divided doses.

OBJECTIVE

To determine whether the current posaconazole dosing guidelines achieve target posaconazole plasma concentrations of 0.7 μg/mL or greater.

METHODS

This retrospective clinical study examined data from patients who received treatment-dose posaconazole and had at least 1 posaconazole plasma concentration measurement.

RESULTS

Data from 33 patients who received posaconazole for the treatment of fungal infections were analyzed. The median age of patients was 11.5 years (range 0.5-23.2). Twenty-one of 33 patients (63.6%) had posaconazole concentrations of 0.7 μg/mL or greater (median 1.4; range 0.7-2.98) at the first measurement. The median posaconazole dosage referenced to total body weight in these patients was 20 mg/kg/day. Patients with concentrations less than 0.7 μg/mL (median 0.4; range 0.025-0.69) received lower posaconazole dosages when referenced to body weight (median 12.9 mg/kg/day; p = 0.02). Of the 12 patients with concentrations less than 0.7 μg/mL, 7 (58.3%) were aged 13 years or older.

CONCLUSIONS

The current dosing approach for posaconazole yielded therapeutic plasma concentrations more frequently in patients younger than 13 years than in those 13 years or older. This difference may be related to the practice of capping adolescent and young adult doses at the suggested maximum adult daily dose. Therefore, we recommend weight-based dosing in all pediatric, adolescent, and young adult patients with cancer, with routine therapeutic drug monitoring to ensure adequate concentrations.

Resumption of high-dose methotrexate after acute kidney injury and glucarpidase use in pediatric oncology patients

BACKGROUND

High-dose methotrexate (HDMTX)-induced acute kidney injury is a rare but life-threatening complication. The methotrexate rescue agent glucarpidase rapidly hydrolyzes methotrexate to inactive metabolites. The authors retrospectively reviewed glucarpidase use in pediatric cancer patients at their institution and evaluated whether subsequent resumption of HDMTX was tolerated.

METHODS

Clinical data and outcomes of all patients who received glucarpidase after HDMTX administration were reviewed.

RESULTS

Of 1141 patients who received 4909 courses of HDMTX, 20 patients (1.8% of patients, 0.4% of courses) received 22 doses of glucarpidase. The median glucarpidase dose was 51.6 U/kg (range, 13-65.6 U/kg). At the time of administration, the median plasma methotrexate concentration was 29.1 μM (range, 1.3-590.6 μM). Thirteen of the 20 patients received a total of 39 courses of HDMTX therapy after glucarpidase. The median time to complete methotrexate excretion was 355 hours (range, 244-763 hours) for the HDMTX course during which glucarpidase was administered, 90 hours (range, 66-268 hours) for the next HDMTX course, and 72 hours (range, 42-116 hours) for subsequent courses. The median peak serum creatinine level during these HDMTX courses was 2.2 mg/dL (range, 0.8-9.6 mg/dL), 0.8 mg/dL (range, 0.4-1.6 mg/dL), and 0.6 mg/dL (range, 0.4-0.9 mg/dL), respectively. One patient experienced nephrotoxicity upon rechallenge with HDMTX. Renal function eventually returned to baseline in all patients, and no patient died as a result of methotrexate toxicity.

CONCLUSIONS

The current results indicated that it is possible to safely resume HDMTX therapy after glucarpidase treatment for HDMTX-induced acute kidney injury.

Neuropathic pain during treatment for childhood acute lymphoblastic leukemia

BACKGROUND

Improved cure rates for childhood acute lymphoblastic leukemia (ALL) over the past 2 decades have allowed greater attention to patients' quality of life. Neuropathic pain (NP) is an unpleasant side effect of chemotherapeutic agents for leukemia, especially vincristine.

PROCEDURE

We retrospectively reviewed the records of 498 patients treated on a single protocol for ALL to investigate the risk factors, the incidence, and the use of therapeutic and prophylactic gabapentin treatment for NP.

RESULTS

White non-Hispanic race was the only patient variable predictive of NP. One hundred and seventy-four of 498 patients (34.9%) experienced 207 episodes of NP; 16% (28 of 174) patients experienced at least one recurrence of pain after the initial episode. No statistical significance was found in the relation between the severity (grade) of the NP episode and the cumulative dose of vincristine (P = 0.45) or the vincristine dose that immediately preceded the diagnosis (1.5 mg/m(2) versus 2.0 mg/m(2) [correction made here after initial online publication], P = 0.59). Of 180 episodes with treatment data, 62.2% (112) and 37.8% (68) were treated with gabapentin or opioids, respectively. The selection of treatment with gabapentin or opioids was not influenced by the pain intensity score at the time of diagnosis of NP (P = 0.91). The mean gabapentin dose used for 112 episodes was 15.5 mg/kg/day (SD 7.9). We found no evidence that gabapentin prevented recurrence of NP.

CONCLUSIONS

Our results highlight the need for prospective randomized studies to elucidate the value of gabapentin regimen for prevention or treatment of vincristine-related pain during treatment of childhood leukemia.

Effect of allopurinol versus urate oxidase on methotrexate pharmacokinetics in children with newly diagnosed acute lymphoblastic leukemia

BACKGROUND

Allopurinol and urate oxidase are both effective in preventing or treating hyperuricemia during remission induction therapy for lymphoid malignancies, but to the authors' knowledge, their effects on concomitant anticancer drug therapy have not been compared.

METHODS

The authors compared plasma methotrexate pharmacokinetics in pediatric patients with newly diagnosed acute lymphoblastic leukemia who received concomitant allopurinol (n = 20) versus those treated with nonrecombinant or recombinant urate oxidase (n = 96) during high-dose methotrexate administration before conventional remission induction therapy.

RESULTS

The minimum plasma concentration of uric acid was significantly (P < .0001) lower after urate oxidase treatment than the concentration after allopurinol treatment. Methotrexate clearance was significantly higher (median, 117.1 mL/minute/m(2) vs 91.1 mL/minute/m(2); P = .019) in patients who received urate oxidase. A higher proportion of patients in the allopurinol group had elevated methotrexate plasma concentrations (36% vs 7%; P = .003) and experienced mucositis (45% vs 16%; P = .003) after methotrexate treatment compared with the urate oxidase group.

CONCLUSIONS

The lower rate of methotrexate clearance in patients who received allopurinol likely reflected a less potent hypouricemic effect of allopurinol, leading to precipitation of uric acid in renal tubules. Hence, during remission induction therapy for lymphoid malignancies, the authors concluded that renally excreted drugs should be monitored closely, especially in patients who are receiving allopurinol.

Recurrent intrathecal methotrexate induced neurotoxicity in an adolescent with acute lymphoblastic leukemia: Serial clinical and radiologic findings

Systemic and intrathecal methotrexate (MTX) are integral components of acute lymphoblastic leukemia (ALL) therapy, but can be associated with neurotoxicity. We describe here the case of an adolescent male with T-cell ALL who developed recurrent episodes of subacute neurotoxicity characterized by slurred speech, emotional lability, and hemiparesis after intrathecal MTX administration. Serial magnetic resonance imaging with diffusion-weighted imaging showed recurrent areas of restricted diffusion within cerebral hemispheric white matter, which correlated chronologically with the administration of intrathecal therapy and severity of clinical symptoms. Resolution of diffusion abnormalities did not preclude further toxicity and a large lesion could cause persisting symptoms.

Late-onset delayed excretion of methotrexate

Pleural effusions, ascites, and renal dysfunction decrease the plasma excretion of methotrexate (MTX). However, it is not known what effect these complications have on MTX clearance when they arise after the plasma MTX concentration has fallen to an undetectable level. We describe the clinical course and pharmacokinetics of MTX in a patient with acute lymphoblastic leukemia who experienced pleural effusions, ascites, and renal failure during the weeks after treatment with high-dose MTX (1.63 g/m2 i.v. over 24 h). The patient's normal initial MTX clearance rate (107 ml/min/m2) was consistent with his undetectable plasma level of MTX on day 9 after the infusion. His plasma MTX concentration then gradually increased as his renal function declined, reaching a peak of 0.72 microM on day 15. This unusual finding of an undetectable plasma MTX concentration that subsequently rose to persistent, potentially toxic levels was explained only by a pharmacokinetic model that accounted both for a third space at the time of treatment and for the subsequent decrease in the systemic elimination rate. Therefore, the finding of a physiologic third space during MTX administration combined with the detection of renal dysfunction in the following weeks should be an indication for prolonged therapeutic drug monitoring.